Extra-intestinal pathogenic Escherichia coli (ExPEC) belong to the normal intestinal microbiota, but can cause pathologies such as urinary tract infection, newborn meningitis and sepsis in humans, or colibacillosis in poultry. Their pathogenic potential can be attributed to the expression of virulence and fitness-associated factors that are required for the establishment of the infection. Important virulence mechanisms involve adhesion, invasion, subversion of host defenses, signaling and direct interference with host cellular functions via toxins and other secreted effectors [Dobrindt U et al., 2008].
Avian pathogenic E. coli (APEC), a subgroup of ExPEC, cause extra-intestinal diseases in chickens known as colibacillosis, which are costly for the poultry industry as they significantly reduce production. Attempts to control colibacillosis through vaccination have only provided partial success. Therefore, it is crucial to identify APEC factors involved in disease and to decipher the molecular mechanism resulting in the establishment of an infection.
ColV plasmids have been strongly associated with APEC, but also to neonatal meningitis-associated E. coli (NMEC), which is another pathotype of ExPEC causing human neonatal meningitis [Peigne C et al., 2009]. ColV plasmids encode genes involved in the synthesis of bacteriocins, including colicin V, iron acquisition and transport mechanisms, avian-like hemolysins, outer membrane proteins and adhesins. These plasmids have been shown to play an important role in the virulence of ExPEC [Skyberg J A et al., 2006]. However, the contribution of individual genes harbored by the ColV plasmids to virulence remains to be elucidated.
Gene hlyF is one of the genes exhibited on ColV plasmids and is widely used as an epidemiological marker for APEC [Ahmed A M et al., 2013] and NMEC [Kaczmarek A et al., 2012]. Although an hemolysin function has been attributed to HlyF, little is known about the exact contribution of HlyF to the virulence of the strain. In a model of infection of the chick embryo, the transcription of the hlyF gene was shown to be strongly up-regulated, suggesting that HlyF could be involved in the establishment of avian extra-intestinal infection. However, hlyF was shown not to be up-regulated in human serum or in urine. Therefore, the precise role of HlyF in virulence of APEC and NMEC remains to be clarified.